MRT is based on the physical phenomenon of magnetic resonance and has been used successfully as an imaging method in medicine and biophysics for more than 15 years. With this examination method the object is exposed to a strong and constant magnetic field. This orients the nuclear spin of the atoms in the object, which were previously random. High frequency waves can now energize this “ordered” nuclear spin to produce a specific oscillation. In the MRT this oscillation generates the actual measurement signal, which is picked up by suitable receiver coils. The use of non-homogenous magnetic fields, generated by gradient coils, means that the measurement object can be spatially coded in all three spatial directions. The method allows free selection of the layer to be mapped, so that sectional images of the human body can be acquired in all directions. MRT, as a sectional image method in medical diagnosis, is primarily characterized as a “non-invasive” examination method by its versatile contrast capability. MRT currently uses applications with a high gradient power, which allow excellent image quality with measuring times in seconds and minutes. The continued constant technical development of components for MRT devices and the introduction of fast imaging sequences opened up an increasing number of areas for the use of MRT in medicine. Real time imaging to assist with minimally invasive surgery, functional imaging in neurology and perfusion measurement in cardiology are just a few examples.
FIG. 1 shows a schematic section through an MRT device according to the prior art. The section shows further components of an inner chamber 21 enclosed by a basic field magnet 1. The basic field magnet 1 contains superconducting magnet coils in liquid helium and is surrounded by a magnet casing 12 in the form of a twin-shell tank. In the inner chamber enclosed in the magnet casing 12 (also referred to as the magnet vessel) the gradient coil 2 is suspended concentrically over support elements 7. The gradient coil 2 comprises three coil segments, which generate three orthogonal gradient fields in the inner chamber 21: a Maxwell coil, which generates a cylindrical gradient field along the longitudinal axis of the patient (z axis) and is therefore referred to as the axial (gradient) coil and two saddle coil pairs rotated through 90° in respect of each other, which are arranged on the cylindrical lateral surface of the gradient coil 2 and are therefore referred to as transverse cylindrical (gradient) coils. Inside the gradient coil 2 a support tube is also concentrically suspended with the high frequency antenna attached to it. The support tube and HF antenna are hereafter referred to as the HF resonator or the body coil BC 13. The gradient coil 2 and body coil 13 thus represent two cylinders inserted one into the other, which either fit together or are at a maximum radial distance—in the form of an air gap—of around 3 cm from each other. The HF antenna has the task of converting the HF pulses emitted by a power transmitter to a magnetic alternating field to energize the atomic cores in the patient 18 and then to receive the core resonance signal, i.e. to convert the alternating field from the presiding core moment to a voltage fed to the receiver branch. The upper part of the body coil 12 is connected mechanically to the magnet casing 12 by means of a cover 29 that is funnel-shaped for design purposes. So-called tabs 30 are mounted in the lower part of the inner chamber 21. The patient 18 is inserted on a patient table 19 over slide rails 17 into the opening or the inner chamber of the system. The patient table is supported on a vertically adjustable support frame 26.
In one possible embodiment of the MRT device—with the new Integrated Field Generator IFG concept—the transverse saddle coil pairs are made up of two half sections, i.e. two shorter tubes, each containing portions of the gradient coil and producing the functionality of a single gradient coil by means of interconnection.